Limit stop



R. D. M COY LIMIT STOP Filed D90. 26, 1942 April 2, 1946. 2,397,557

lllll n I! III luv" INVENTOR Patented Apr. 2,

' UNITED STATEQ PATENT OFFECE LIMIT STOP Rawley D. McCoy, Bronxville, N. Y., assignor to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a corporation oi? New York Application December 26, 1942, Serial No. 410,294

13 Claims.

age may then be employed to control the direc-- tion and speed of a suitable driving means, such as a motor, which drives the controlled object in such a direction as to reduce the control signal voltage to zero, at which time theobject will be at its desired position. Some kind of a follow-up system is also driven synchronously withthe controlled object in order to provide a means of measuring the displacement of the object from voltages proportional thereto.

In most cases there are certain limiting positions of travel which it is imperative that the controlled object not exceed, irrespective of the value or direction of the control signal voltage. These limitations may be imposed, for example, by restrictions in the mounting equipment of the controlled object,v which render mechanically impossible any motion beyond a certain point. In such a situation, when the. controlled object approaches its limiting position, it is desirable to V render inefiective the control of the signal voltage, and at the sametime to strongly brake the motor so that the object will come to rest before damage is done. When the object is thus at rest in its limiting position, the motor should be under the control of the signal voltage only for voltage signals tending to produce rotation in the direction away from the limit.

- its desired position, and driving control signal Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawing wherein the invention is embodied in concrete form.

I attain these objects by mechanism illustrated in the accompanying drawing, in which, l

The single figure is a combination wiring diagram and perspective drawing illustrating a preferred embodiment of the present invention.

Referring now to the figure, wherein the system of limit stops of the present invention is shown for the sake oi concreteness as employed in a Ward-Leonard type of remote control system, a control signal voltage is shown applied to the grids l and 2 of the conventional push-pull D. C. amplifier circuit 5. This control signal voltage corresponds in polarity and magnitude to the sense and magnitude of the displacement of the controlled object 4 from its desired position. This control voltage, having been amplified in amplifier 5, is then applied across the field winding 6 of the D. 0. generator I. I

The generator 3 is shown as driven from a shunt-wound direct current motor 8, which is energized from a, constant source of direct cur-- rent as by leads '9, '9. One output terminal it! of the generator I is directly connected to one terminal ll of the direct current driving motor 12, whereas the other output terminal to of the generator I is connected to terminal 08 of the motor l2 through three parallel circuits which a pear between the points is and I5.

The lower circuit connecting the points M and It comprises a resistor l6 and a relay coil ll. Energization of the relay coil it is adapted to close the normally open contacts it, it against the operation 01 the spring l9, thereby causing Accordingly, it is the primary object of the a short circuit across the points to and 2t, and consequently across the armature of the driving motor i2.

Also connected in series across the points it 1 and I5 are two sets or rectifiers 26,22. These rectifiers, which may, for example, be of the welllmown selenium oxide or copper oxide type, form a very.highresistance to current now through them in one direction, the backdirection, while constituting a very low reslstancaapproaching a short circuit. to current fiow in the opposite, or forward, direction. Thetorward direction of.

the rectifiers 2t, 22 is indicated by the direction of the arrows. As shown, the rectifiers are con- Another object of the invention is to provide a system of limit stops particularly useful with a Ward-leonard type or remote control system. 65 A series circuit is nected in the circuit so that their forward directions oppose, the forward direction of each being toward the mid-P int 35.

also made acrossthe points I4 and I through the twoi'pairs of normally closed contacts 23, 23' and 24, 24. As shown, these two pairs of contacts are normally maintained in their closed position through the action of the springs and 26, respectively but may be opened by the cams and 29, respectively. Mid-point 36 between the two pairs of contacts 23, 23' and 24, 24' is electrically connected to mid-point between the two sets of 'rectifiers 2| and 22.

The direct current driving motor I2, the, field winding 31 of which is energized from aconstantsource of direct current, as by leads 38, 38, posi tions the controlled object 4 as by way of shaft 21.

of follow-up mechanism (not shown), from which the control signal voltage may be obtained} Driving motor I2 is also-shown -as actuating two cams 29 and'30 through bevel gears3l, 32, 33 and 34. The cams 28' and 30 and their associated gearing are so designedthat the contacts 24, 24' are caused to open at the limiting posi-v Shaft 28, also actuatedfrom the driving motor I2, is provided'in order to, drive some sort.

current must flow through the rectifiers 22 in a direction opposite to its forward direction, thereby producing a high voltage drop across the points I4 and I5.

In this way a high. voltage will build up across thepoints I4 and I5-and will partially be applied to the relay 'coil I'I. zation of relay coil I1 is suflicient to cause the contacts I8, I 8' to close, short-circuiting the armature terminals II and I3 of the motor I2 and causing dynamic braking of the motor. At the tion of the controlled objectlin one direction,

while th contacts 23; 2,3 are caused to open at the limiting position of the controlled object in the opposite direction.- I

In operation, thereforeg'the' contacts 23, 23' and 24,24 will be closed at all positions of the controlled object 4 intermediate to the'limiting positions. In such case, since a short-circuit will be eflfected across thepoints 54, I5, the relay l1 will not be energized, and the -contacts I8, l8v will same tim the control voltage generated across the output terminals III- and of the generator I, being still of, the same polarity, encounters. only a high resistance current path either through the resistance I6 and relay coil I1 or alternatively through the'rectifiers 22 in a direction opposite to its forward direction. Thus, with contacts 24, 24' open, a. control signal voltage which would produce displacement of the. controlled object 4 in sucha direction as to exceed the limiting position ofthe object will maintain th contacts 18, I8 closed, thus renderingineilective the control signal voltage;

be open. Therefore, the voltage generated at the terminals I0 and 40 of the generator I will be applied directly to the armature terminals 'II and I3 or th 'motor I2, and the system will operate in the normal manner as a Ward-Leonard type oi'd'emote control system. s

Thus, in normal operationthe signal voltage, indicative of the amount and direction of the displacement of the controlled object 4 from its de- On the other hand, a control signal voltage of such a polarity as wouldnormally backthe controlled object off away from its limiting position condition with contacts 24, 24' and 23, 23' closed sired position, is linearly amplified in the pushpull amplifier circuit 5 and'applied to th field winding 8 of the direct current generator I. The generator I, being drivenat a substantially con-=- stant speed from motor 8 will produc a'propor-' tionate, but further amplied, volta'ge across its output terminals I0 and 40. Thisgen'erated voltage is then applied to the armature of the driving motor I2, the field of which is energized from a constant source of direct current. The driving motor I2 will therefore drive the controlled object 4 and its associated follow-up mechanism, at a speed and in a direction corresponding to the magnitude and-polarity of the voltage applied to the motor terminals Hand I3, and consequently also corresponding to the magnitude and polarity of the original control signal voltage. The motor I2 will continue to drive the object in response to the control signal voltage, until the desired position. is reached," at which time the control voltage will have been reduced to zero.

It will now be assumed that the motor I2 has driven the controlled object 4 to the. particular limiting position at which the cam 29 will cause the contacts 24, 24 to open',,and that the control and contacts I8, I8 open.

Should a limiting position be reached in the opposite direction to that just described, it is obvious that cam 30 will cooperate with contacts 23, 23', rectifiers 2|, relay coil I1, and contacts I8, I8 to produce a similar polarity responsive control over the motor I2.

It will be understood that the cams 29 and 30 need not beactuated only in response to the position of th controlled object 4, but may also of the control signal voltage.

signal voltage is still of such a polarity as would;

normally cause the controlled object to continue to be driven on past this limiting position. These are the conditions illustrated in Fig. 1. It will be understood that the polarity of the control ,voltage required to produce rotation of the mo tor in such a direction is such as would cause in its amplification.

be controlled from the rate of said controlled object and from any other physical conditions which it is desired to set in.

The circuit arrangement disclosed, consisting of the three parallel branches between the points I4 and I5, need not necessarily be connected between the motor I and generator l2, but could equally well be inserted in series with the original control signal voltage, or at any subsequent stage It isconsidered advantageous, however, to locate the circuit arrangement as shown in order to insure operation of the limit stop in case a continuous voltage should ever be applied to the motor I2, irrespective of the value This condition might occur, for example, upon failure of any of the intermediate amplifier stages.

Although the present invention has been illustrated for concreteness in a Ward-Leonard type of remote control system, it could equally well be applied to any electrical remote control system wherein a motor drives a controlled object in a direction corresponding to the sense of a control current flow from the point M to th point I5;

Accordingly, since contacts 24, 24' are now open,

signal voltage.

As many changes could be made in the above construction and many apparently widely differ- The resulting energi ent embodiment of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A limit stop for a remote control system wherein a motor normally drives an object to a' desired position in response to a signal voltage comprising a relay arranged in the circuit so that actuation of the relay coil is adapted to shortcircuit the armature of said motor, a uni-directional circuit element in series with said armature and in parallel with said relay coil. and. means responsive to the position of said object for short-circuiting said element.

2. A limit stop for a remote control system wherein a motor normally drives an object to a desired position in response to a signal voltage, comprising a relay, means for short-circuiting the armature of said motor upon actuation of said relay, a rectifier in series with said armature and in parallel with said relay coil, and .means for short-circuiting said rectifier except when a predetermined set of conditions, including the position of said object, has been obtained.

3. A limit stop for a remote control system wherein a motor normally drives an object to a desired position in response to a signal voltage. comprising a relay arranged in the circuit so that actuation of the relay coil is adapted to short-circuit the armature of said motor, a rectifier in series with said armature and in parallel with said relay coil. switching means for shortcircuiting said rectifier, and a cam responsive to the position of said object for actuating said switching means.

4. A limit stop for a remote control system wherein a motor normally drive an object to a desired position in response to a signal voltage. comprising means responsive to the sense of said signal voltage for short-circuiting the armature of said motor, switching means for rendering ineffective said former means, and cam means responsive to the position of said object for actuating said switching means.

5. A limit stop for a remote control system wherein a motor normally drives an object to a desired osition in response to a signal voltage, comprisin a circuit arrangement in series with the armature of said motor, said arrangement consistin of a first switch, a unidirectional circuit element. and a relay coil, all connected in parallel. cam means responsive to the position of said obiect for actuating said first switch, and a second circuit arrangement connected across the armatu e of said motor. said second circuit consisting of a second switch responsive to the energization of said relay coil.

6. A l mit stop for a remote control system wherein motor normall drives an object to a desired position in response to-a signal voltage, comprising a circuit arrangement in series with the armature of said motor, said arrangement consisting of a first switch, a rectifier, and. a relay coil. all connected in parallel, cam means responsive to the position of said object for actuating said first switch, and a second circuit arrangement connected across the armature of said motor, said second circuit consistingofa second switch responsive to the energization of said relay coil.

'7. A limit stop for a remote control system wherein a motor normally drives an object to a desired position in response to a signal voltage, comprising means responsive to the sense of said signal voltage for short-circuiting the armature of said motor, and means responsive to the position of said object for rendering ineffective said former means.

8. A limit stop for a remote control system wherein a motor normally drives an object to a desired position in response to a signal voltage, comprising a relay arranged in the circuit so that actuation of the relay coil is adapted to shortcircuit the armature of said motor, control means responsive to the sense of the signal voltage for actuating said relay, and means responsive to the position of said object for rendering ineffective said control means.

9. A system of limit stops for a remote control system wherein a motor normally drives an object to a desired position in response to a signal voltage, comprising two normally short-circuited unidirectional circuit elements connected, with the armature of said motor, means responsive to the position of said object for selectively removing the short-circuited condition of one or the other of said elements, and means responsive to.

the potential across both of said elements for short-circuiting the armature of said motor.

10. A limit stop arrangement for a remote controlled object comprising a motor for moving the object back and forth between two limit stops, a control circuit for the motor effective to control the direction of the motor according to the direction of the current in the circuit, a pair of rectifiers oppositely connected in the circuit, normally closed contact means individual to the rectifiers forming a shunt about each rectifier, means controlled by the object on reaching either limit stop to operate an appropriate one of the contact means thereby opening the shunt about the associated rectifier, the rectifier being so poled as to cut oif current of such direction as to tend to operate the motor to drive the object beyond the limit stop.

11. A limit stop arrangement for a remote controlled object comprising a motor for moving the object back and forth between two limits, a control circuit for the motor effective to control the direction of the motor according to the direction of the current in the circuit, a pair of rectifiers oppositely connected in the circuit, a shunt for each rectifier comprising a pair of normally closed contacts, means for opening one or the other pairs of contacts as the object reaches either of the respective limits thereby removing the shunt from the associated rectifier, said rectifier being so poled as to cut off the current in the control circuit operating the motor.

12. A limit top arrangement according to claim 11, in which opposite poles of the rectifiers are connected together and in which both rectifiers are shunted by a circuit including a relay, the relay being operable on the opening of either pair of contacts, the relay when operated being adapted to brake the motor.

13. A limit stop arrangement according to claim 11, wherein the control circuit is such that when one pair of contact means is open, only current in reverse direction therein will operate the motor, whereby subsequent motion of the object must be toward the more remote limit.

RAWLEY D. MCCOY. 

